C++ 类的聚集和浅拷贝与深拷贝

1.类的聚集

类的成员中含有某类的指针，这种类叫类的聚集。又被称为“远程所有权”（remote ownership）。

该类的对象的数据将存放在对象外边，对象中只存放数据的地址。数据可以是数组、对象等。



2.浅拷贝与深拷贝

浅拷贝

–实现对象间数据元素的一一对应复制。这是拷贝构造函数的本能。当数据元素是指针的时候，则出问题。

深拷贝

–当被复制的对象数据成员是指针类型时，不是复制该指针成员本身，而是将指针所指的对象（区域）进行复制。

对象的浅拷贝

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//对象的浅拷贝

#include<iostream>

using namespace std;

class Point

{

public:

Point()

{ X=Y=0; cout<<"Default Constructor called.\n";}

Point(int xx,int yy)

{ X=xx; Y=yy; cout<< "Constructor called.\n"; }

~Point() { cout<<"Destructor called.\n"; }

int GetX() {return X;}

int GetY() {return Y;}

void Move(int x,int y){ X=x; Y=y; }

private:

int X,Y;

};

class ArrayOfPoints //这个类叫“控制类”

{

public:

ArrayOfPoints(int n) // 按照指示创建指定个数的对象

{

numberOfPoints = n;

points = new Point
;

}

~ArrayOfPoints()

{

cout<<"Deleting..."<<endl;

numberOfPoints=0;

delete[] points;

}

Point& Element(int n)

{

return points
;

}

private:

Point *points; //类内只保存对象数组的首址

int numberOfPoints; //对象的个数

};

void main()

{

int number;

cout << "Please enter the number of points:";

cin>>number;

ArrayOfPoints pointsArray1(number);

pointsArray1.Element(0).Move(5,10);

pointsArray1.Element(1).Move(15,20);

//对象的浅拷贝

ArrayOfPoints pointsArray2(pointsArray1);

//输出对象的值

cout<<"Copy of pointsArray1:"<<endl;

cout<<"Point_0 of array2: "

<<pointsArray2.Element(0).GetX()

<<", "<<pointsArray2.Element(0).GetY()<<endl;

cout<<"Point_1 of array2: "

<<pointsArray2.Element(1).GetX()

<<", "<<pointsArray2.Element(1).GetY()<<endl;

//对象1的值改变同时也会改变对象2的值

pointsArray1.Element(0).Move(25,30);

pointsArray1.Element(1).Move(35,40);

//输出对象的值

cout<<"After the moving of pointsArray1:"<<endl;

cout<<"Point_0 of array2: "

<<pointsArray2.Element(0).GetX()

<<", "<<pointsArray2.Element(0).GetY()<<endl;

cout<<"Point_1 of array2: "

<<pointsArray2.Element(1).GetX()

<<", "<<pointsArray2.Element(1).GetY()<<endl;

}

运行结果：

Please enter the number of points:2

Default Constructor called.

Default Constructor called.

Copy of pointsArray1:

Point_0 of array2: 5, 10

Point_1 of array2: 15, 20

After the moving of pointsArray1:

Point_0 of array2: 25, 30

Point_1 of array2: 35, 40

Deleting...

Destructor called.

Destructor called.

Deleting...（同一块空间被释放了两次）

接下来程序出现异常，也就是运行错误。



对象的深拷贝

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//对象的深拷贝

#include<iostream>

using namespace std;

class Point

{

public:

Point()

{ X=Y=0; cout<<"Default Constructor called.\n";}

Point(int xx,int yy)

{ X=xx; Y=yy; cout<< "Constructor called.\n"; }

~Point() { cout<<"Destructor called.\n"; }

int GetX() {return X;}

int GetY() {return Y;}

void Move(int x,int y){ X=x; Y=y; }

private:

int X,Y;

};

class ArrayOfPoints //这个类叫“控制类”

{

public:

ArrayOfPoints(int n) // 按照指示创建指定个数的对象

{

numberOfPoints = n;

points = new Point
;

}

//不能用默认的拷贝构造函数，必须重写了

ArrayOfPoints(ArrayOfPoints& pointsArray);

~ArrayOfPoints()

{

cout<<"Deleting..."<<endl;

numberOfPoints=0;

delete[] points;

}

Point& Element(int n)

{

return points
;

}

private:

Point *points; //类内只保存对象数组的首址

int numberOfPoints; //对象的个数

};

//拷贝构造函数

ArrayOfPoints::ArrayOfPoints(ArrayOfPoints& pointsArray)

{

numberOfPoints = pointsArray.numberOfPoints;

//申请新的空间

points=new Point[numberOfPoints];

for (int i=0; i<numberOfPoints; i++)

//把值拷贝过来

points[i].Move(pointsArray.Element(i).GetX(),

pointsArray.Element(i).GetY());

}

void main()

{

int number;

cout << "Please enter the number of points:";

cin>>number;

ArrayOfPoints pointsArray1(number);

pointsArray1.Element(0).Move(5,10);

pointsArray1.Element(1).Move(15,20);

cout << "test\n";

//对象的深拷贝

ArrayOfPoints pointsArray2(pointsArray1);

cout<<"Copy of pointsArray1:"<<endl;

cout<<"Point_0 of array2: "

<<pointsArray2.Element(0).GetX()

<<", "<<pointsArray2.Element(0).GetY()<<endl;

cout<<"Point_1 of array2: "

<<pointsArray2.Element(1).GetX()

<<", "<<pointsArray2.Element(1).GetY()<<endl;

//深拷贝对象2的值不会因对象1的值改变而改变

pointsArray1.Element(0).Move(25,30);

pointsArray1.Element(1).Move(35,40);

cout<<"After the moving of pointsArray1:"<<endl;

cout<<"Point_0 of array2: "

<<pointsArray2.Element(0).GetX()

<<", "<<pointsArray2.Element(0).GetY()<<endl;

cout<<"Point_1 of array2: "

<<pointsArray2.Element(1).GetX()

<<", "<<pointsArray2.Element(1).GetY()<<endl;

}

运行结果：

Please enter the number of points:2

Default Constructor called.

Default Constructor called.

Default Constructor called.

Default Constructor called.

Copy of pointsArray1:

Point_0 of array2: 5, 10

Point_1 of array2: 15, 20

After the moving of pointsArray1:

Point_0 of array2: 5, 10

Point_1 of array2: 15, 20

Deleting...

Destructor called.

Destructor called.

Deleting...

Destructor called.

Destructor called.

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使用动态存储分配的类要重写拷贝构造函数！